Down-hole annular pressure is a well-known measurement in the technology area of wellbore drilling. Down-hole annular pressure data may be used to identify undesirable drilling conditions, suggest remedial procedures, and prevent serious problems from developing. For example, with accurate annular pressure data in real-time, drillers can apply conventional drilling practices more effectively to potentially reduce both rig time and the number of casing strings. In particular, SPE publication No. 49114 discusses how, with real-time down-hole annular pressure while drilling (“APWD”) measurements, drillers can more effectively maintain the equivalent circulating density (“ECD”) and equivalent static density (“ESD”) within a desired range in order to prevent lost circulation and maintain wellbore integrity by managing swab, surge and gel breakdown effects.
However, it may not be always possible to provide real-time down-hole APWD measurements to drillers, in particular during pipe connections when the drilling fluid circulation pumps are turned off (a “pumps-off” condition). Instead, Canadian patent No. 2,298,859 discloses a method that provides near real-time advantage of APWD measurements taken during pipe connections. APWD data are measured, stored and even processed in the bottom-hole assembly during a pumps-off condition for subsequent communication of a reduced amount of data to drillers at the surface. More recently, wired drill pipe (“WDP”) technology has been offering along-string APWD measurements in real-time. For example, the industry report published on the September 2011 issue of World Oil describes a well drilling operation where battery-powered tools were connected down-hole to a WDP network to continuously transmit down-hole APWD data even when no circulation was present. In this example, an integrated managed pressure system allowed drillers to instantaneously and continuously control circulating pressure within a 30-psi window while drilling, and to control pressure changes within a 100-psi window during drill pipe connections.
The full benefits of APWD data availability in real-time may not have been achieved yet because drillers still rely on approximative rules for operating drilling equipment and control the variations of APWD. These rules, while having possibly wide application, may not be intended to be strictly accurate or reliable in every situation. Typically, these rules yield to operations of wellbore drilling equipment that are too conservative and less economical. However, in some cases, these rules may be too aggressive, and excessive drilling rate of penetration (“ROP”) may compromise wellbore stability or excessive speed of the drill string may generate flow of formation fluid into the wellbore during tripping operations such as when tripping out of the hole.